低铅暴露对大鼠海马突触可塑性范围的影响

EFFECT OF CHRONIC LEAD EXPOSURE ON THE RANGE OF SYNAPTICPLASTICITY IN DENTATE GYRUS (DG) OF RAT HIPPOCAMPUS IN VIVO

长时程增强(LTP)和长时程抑制(LTD),作为突触可塑性变化的两种主要形式 ,被认为是学习记忆的可能机制。突触可塑性范围可以定量的表征突触可塑性的变化。应用在体电生理技术 ,在同一只动物上记录LTP和LTD ,研究了发育过程中慢性铅暴露对大鼠海马齿状回颗粒细胞突触可塑性范围和双脉冲易化的影响。对照组的LTP、LTD的幅度分别是187.9±6.2 %(n=7) ,85.2±1.6 % (n=7) ,而铅处理组分别为140.5±1.2 %(n=7) ,102.8±3.8 %(n=7)。与对照组相比,铅处理组的LTP的幅度降低了47.4 %,LTD的诱导几乎完全被铅损伤。先诱导出LTP后再通过低频刺激则可以在铅处理组诱导出LTD(81.5±2.2%(n=7)) ,但远远小于对照组 (66.8±4.3 %(n=7))。对照组突触可塑性范围是103.1±11.5 % (n=7) ,是铅处理组突触可塑性范围(37.7±9.6 %(n=7))的2.7倍。在对照组 ,双脉冲易化反应是从脉冲间隔20ms时开始 ,而铅处理组则是从50ms开始。当脉冲间隔为70ms时 ,两组的双脉冲易化幅度均达到最大值 ,但易化的强度有显著的差异 ,分别为211.6±32.2 %(n=7) ,111.1±26.9 %(n=7)。结果表明 :铅显著地抑制了大鼠海马齿状回颗粒细胞的双脉冲易化效应 ,降低了双脉冲易化的间隔范围和突触可塑性范围。这可能是铅损伤学习记忆功能的机制之一。

Long-term potentiation (LTP) and long-term depression (LTD), two forms of synaptic plasticity, are believed to underlie the mechanism of learning and memory. The range of synaptic plasticity is defined as the sum of amplitudes of LTP and LTD. Previous studies have demonstrated that low-level lead exposure can decrease the range of synaptic plasticity of EPSP in the different slices in vitro. The present study is carried out to investigate the variation of the range of synaptic plasticity of population spike (PS) and paired-pulse facilitation (PPF) in hippocampal dentate gyrus in vivo following the developmental lead-exposure by electrophysiological techniques. 2.1 The amplitudes of PPF are greater in control group than that in lead-exposed group. The onset inter-pulse interval (IPI) of PPF in the control and lead-exposed groups are 20ms and 50ms respectively. When the IPI is at 70ms, PPF of PS in both control and lead-exposed groups reach the maximum: 211.6±32.2%(n=7),111.1±26.9%(n=7) respectively. Compared with the control group, the lead-exposed group decreased by 100% in the amplitude of PPF of PS. The amplitude and range of IPI in the pared-pulse facilitation are impaired by lead. 2.2 The amplitude of LTP in the control group is 187.9±6.2%(n=7),and the lead-exposed group is 140.5±1.2%(n=7),less than 47.4% of the control one. There is almost no LTD of PS in lead-exposed group, while the amplitude of LTD in control is maintained at 84.8±4.4%(n=7).After tetanic stimulation, low frequency stimulation can evoke LTD, which is much larger: LTD in control one is 66.8±4.3%(n=7), and in lead one is 81.5±2.2%(n=7). 2.3 The range of synaptic plasticity of PS in control and lead-exposed are 103.1±11.5%(n=7),37.7±9.6%(n=7),respectively. It has a decrease by 64% in the range of synaptic plasticity of PS in lead-exposed group. The results demonstrate that low-level lead-exposure could reduce the range of synaptic plasticity, which might underlie the dysfunction of learning and memory by chronic lead-exposure.